Periodontal disease affects the majority of adults and is the major cause of tooth loss in the western world. Although cross-sectional studies in human indicate that the subgingival microbiota in periodontitis differs from that observed in gingival health, disease initiation cannot yet be attributed to specific groups of microorganisms. This is primarily due to the inability to assess disease activity in humans and the improbability of monitoring the microbiota prior to and during the initiation of periodontitis in humans. Ligature-induced periodontitis in the cynomolgus monkey has been characterized microbiologically and has been established as an appropriate model for studying the initiation and progression of periodontitis. This proposal seeks to continue this effort by focusing on those organisms which change in the subgingival microbiota at the earliest detectable initiation of periodontitis, and those organisms which appear to be essential to disease development. New techniques for culturing spirochetes will be used to determine the association of microscopic and cultural counts of spirochetes with periodontitis in a well controlled situation in which a progressing periodontitis can be readily monitored. New subtraction radiographic techniques for monitoring bone loss and new biochemical techniques for characterizing constitutive enzymes of slow growing non-fermentative anaerobes will e used to study the total cultivable microflora just prior to the initiation of bone loss and just after bone changes are detectable. This approach will allow the determination of all components of the cultivable microbiota which change at the initiation of periodontitis, even prior to it becoming clinically detectable. In addition, previously established procedures for selectively altering the micribiota to a nonpathogenic state will be used to determine which organisms are essential to disease initiation and progression. The combined rsults of these studies will provide an assessment of the role of spirochetes in periodontitis and a detailed comparison of microbiotas associated with progressing periodontitis and non-progressing periodontal conditions.